Motor-starter.



' G. MASC/mlm 9 A` CONTARDI.

MOTOR STARTER.

APPLICATION FILED MAY 4. |915- 1,802,400. Patented Apr. 29, 1919.

lullinV v Byw-waagm i TOHWEY GIOVANNI MASCARINI AND ANGELO CONTABDI, F MILAN, ITALY.

MOTOR-STARTER.

Specification of Letters Patent.

Patented Apr. 29, 1919.

Original application led January V3, 1,914, Serial No. 810,177. Divided and this application led May 4,

1915. Serial No. 25,847.

of Milan, in the Kingdom of Italy, have in vented certain new and useful Improvements in Motor-Starters, of which the following is a specification. v

This invention relates to rheostats vfor starting triphase motors and the object of the vinvention is to provide an improved rheost-at utilizing iron sulfid for the resist- -ance elements thereof. The electrical resistance of ironl sulfid varies from about 65 to 1 when itstemperature varies from 14 to about 160"y C. Hence this substance is very suitableA for the construction of automatic rheostats 'whose resistance diminishes as the temperature increases. Another object of the invention is to provide a novel arrangement and combination of circuits and apparatus for automatically controlling the secondary circuit of asynchronous polyphase motors. y

To this end the invention consists of a rheostat formed by three elements of iron vsulfid the electrical resistance of which is determined by the resistance necessary for starting and the dimensions ofwhich are 'such that the gradual increase of the temperature due tothe electrical energy which is converted step by step into heat produces a variation of resistance giving rise to a uniform increase in the speed of the motor. An automatic rheostat is thus obtained which subsequently permits of short circuiting the rotor. The invention further consists in the construction and arrangement hereinafter more fully described.

Heretofore the obj ect of the present application was aimed at by some inventors, but to this purpose either resistances of the ordinary type were employed, their self-reduction taking place step by step, or the reduction of the resistance was effected by an increase oi' pressure` exerted on resistance disks, or magnetite was employed. Moreover, our Patent No. 1,185,227, granted May 30, 1916, discloses a rheostat having a resist-- ance element consisting of a homogeneous body of metallic sultid, and more especially of iron sulid` while the present invention covers the use cfa resistance of metallic sultid, and more especially of iron sulld. in combination with means for automatically opening and closing the connections for the purpose of starting triphase motors. The present application is a division of application Serial No. 810,177, filed January 3, 1914, which eventuated in our .Patent No. 1,185,227 above referred to. A

Figure 1 is a diagram showing an arrangement in which the rheostat is separate from the motor.

Fig. 2 is a diagram showing an arrangement in which the apparatus and circuit connections are carried on the motor shaft, and the necessity of slip rings is obviated.v

E represents the three elements of the rheostat connected by the conductors D'to the brushes of the slip rings C of the motor B. In shunt with the circuit D and in series with the resistance P which may be graduated, there are three vsolenoids M star or mesh-connected, adapted to attract cores L which are also arranged to be attracted by three other solenoids N in shunt with the supply circuit A of the motor, between the latter and the switch y. The three cores L are connected and made integral with each other by means of a yoke K which carries contacts I; when the yoke moves downwardly these contacts short-circuit the circuit D thus cutting out the rheostat E. A spring O is provided for lifting the yoke' and serves to open the short-circuit and the motor is then ready to start. lVhen the motor switch is closed, the cores which are .raised by the spring O are within the solenoids M. The latter are then energized-due to the potential difference between the slip rings of the motor, whereas the solenoids N are energized bythe current due to the voltage of the supply circuit of the motor, the parts being so arranged and adjusted that the cores are attracted and held by the solenoids M. As the speed of the motor in- I creases, the voltage decreases as well as the" frequency in the solenoids M; while in the 100 solenoids N these elements remain constant and therefore the torce of attraction also remains constant. The auxiliary resistance'sP may be adjusted in such a manner that at a predetermined speed of the motor, the action 105 ot thesolenoids N exceeds the gradually1 decreasing action` ot' the solenoids M the former thus attracting the cores L and therefore producing short-circuiting ot' the rotor.

.\t the incluent the .switeh'g/ is opened, the 110 action of the solenoids ceases, the spring O raises the yoke Kand replaces the rheostat thermic rheostat arranged in a circular manner and star or mesh-connected, and joined j by the conductors D to the ends of the rotor winding. In shunt to the ends of the rheo-` stat, there are three electromagnetsM against which the armatures L are caused to bear by the springs O, these armatures being v mounted on the balancers F pivoting about Q. The three balancers F are connected with one another by leads S or are elec/trically connected with the metallic mass of the shaft. When the balancers ivot the arms I will -come into Contact with contacts G connecting the ends of the rheostat and short-circuiting the rotor.

Assuming that the motor starts, the balancers will tend to pivot owing to the cen- 'trifugal action of the members Carrying the armatures L, but this oscillation is partly prevented by the action of the springs O, and partly by the attraction of the electromagnets M.v

By designing the latter and the springs in an appropriate manner and varying slightly the weight yof the arms I of the balancers, the armatures L will, at a predetermined speed of the motor, move away from the electro-magnets and the balancers will short-circuit the rotor. As the motor stops the action of the Springs O will open the short-circuit and the motor will again be ready to start.

The advantages obtained with the described devices are varied and are of great importance.

What we claim and desire to secure by.

Letters Patent of the United States is 1. In a controlling device for alternating current motors, a self-reducing resistance of iron sulid connected in the secondary circuit, switching means adapted to short circuit said reslstance, and electro-magnetic means connected in shunt to said resistance, arranged to prevent the short circuiting operation of said switching means until the rcduction of said resistance to a predetermined minimum.

2. In combination with an alternating cur u rent induction motor having a rotor, shaft and secondary circuit conductor related in fixed relation t0 each other; a rheostat for said secc-ndary. circuit having self-reducing resistance elements carried by said shaft, means for shunting said rheostat out of said secondary circuit, electro-magnetic means electrically connected with said rheostat and responsive to variations in the resistance thereof, and means rotated by said shaft and operated upon conjointly by centrifugal force and said electromagnet means to actuate said shunting means.v

3. In a controlling device for asynchronous triphase motors, a rheostat having iron suld resistance elements inserted in the rotor circuit, switching means `adapted to short circuit said elements, and electro-magnets subjected vto the dierence in potential between the terminals of the rotor Winding` said resistance elements, switching means and electro-magnets being carried by the rotor shaft, said switching means being adapted to be actuated by centrifugal force, and said eleotro-magnets being adapted to prevent the short circuiting operation of said switching means until the reduction of said resistance to a predetermined minimum.-

4. In a controlling device for asynchronous triphase motors, a rheostat having iron suld resistance elements inserted in the rotor circuit, switching means adapted to short circuit said elements, electro-magnets subjected to the difference in potential between the te rminals of the rotor winding, said resistance elements, switching means and electro-magl' nets being carried by the rotor shaft, said switching means being adapted to be actuated by centrifugal force, said electro-magnets being adapted to prevent the short circuiting operation of said switching means until the reduction of said resistance to a predetermined minimum, and springs adapted to return said switching means to their inoperative position When the speed of the rotor falls below a predetermined value.

In testimony whereof we affix our signa tures 1n presence of two wltnesses.

GIOVANNI MASCARINI. ANGELO CONTARDI.

Witnesses:

B. CARLO SALVATOR, LYL'E RoBB. 

